Posted: Tue May 26, 2020 4:32am
In a small apartment, your electricity supply is probably only 3.5 kw. Draw more current than that and you will trip the meter.
Most instantaneous hot water heaters draw much more than that, e.g. up to 24 kw. Even if the wiring is good enough to support such a high current, which is very unlikely, you'd have to pay for an initial boletín to confirm the allowable current, and the standing charge on your electricity bills would shoot up dramatically.
You can get a 3.5 kw heater, but even that would mean you couldn't have another electrical appliance in use at the same time. Such a low rated heater might provide enough hot water for washing, but I very much doubt whether it would provide enough for a shower:
https://www.amazon.es/Stiebel-Eltron-185411-Calentador-el%C3%A9ctrico/dp/B000ONRA4M/ref=sr_1_fkmr0_2?__mk_es_ES=%C3%85M%C3%85%C5%BD%C3%95%C3%91&dchild=1&keywords=Stiebel+Eltron+DHM3&qid=1590459701&sr=8-2-fkmr0&tag=cstareg0f-21